The intense commercialization of metallocene polyolefin catalysts has led to widespread interest in the design of non-metallocene, homogeneous catalysts. This field is more than an academic curiosity as new, non-metallocene catalysts may provide an easier pathway to currently available products and may also provide product and process opportunities which are beyond the capability of metallocene catalysts. In addition, certain non-cyclopentadienyl ligands may be more economical due to the relative ease of synthesis of a variety of substituted analogs.
Thus there is a need in the art for new olefin polymerization catalysts and the polymers they produce. This invention identifies a new family of catalysts that can be used to produce polyolefins, particularly polyethylenes.
WO 97/02298, WO 96/33202 and Fuhrmann et al, Inorg. Chem. 35:6742-6745 (1996), each fully incorporated herein by reference, all disclose nitrogen containing single site like catalyst systems.
WO 99/01460, fully incorporated herein by reference, discloses the use of transition metal compounds comprising bidentate ligands containing pyridine or quinoline moieties and mixtures thereof with activators to polymerize olefins. For example, [[1-(2-pyridyl)N-1-methylethyl]-[1-N-2,6-diisopropylphenylamido]] zirconium tribenzyl is combined with modified methyl alumoxane in the gas phase to produce ethylene/hexene copolymers.
Furthermore, U.S. Pat. No. 6,187,712 B1, fully incorporated herein by reference, discloses a catalyst composition for the polymerization of olefins that comprises a mono- or biscyclopentadienyl catalyst precursor comprising at least one protected hydride and/or protected hydrocarbyl ligand such as tetrahydroborate bound to a metal atom. A typical example of a catalyst precursor disclosed in the patent is methylcyclopentadienylzirconium tris(tetrahydroborate).
It has now been found that transition metal compounds comprising both polydentate, heteroatom containing ligands and protected hydride and/or hydrocarbyl ligands combined with a cocatalyst can effectively catalyze the polymerization of olefins.